Design of digital FM radio using single chip microcomputer + CXA1019S + phase-locked loop BU2614

4.3 Power-off data storage procedure

     This part mainly includes: (1) Read the data stored in 93C46 to the corresponding position every time the machine is turned on. (2) After each cycle scan and function query in the main program, write the current value and stored data into the 93C46 chip. The two parts of the program are as follows:

(1) Program to read data from 93C46

LCALL INSB ; Read the value before the last shutdown

          MOV A,#80H

          ORL A,#80H

          LCALL WRI ;Call write instruction

          NOP

          NOP

          LCALL RDI ; read and write data in 31H

          MOV 31H,A

          LCALL RDI

          MOV 2FH,A ; read and write data in 2FH

          SETB P3.2

          NOP

          MOV R0,#0AH

          MOV R1,#4AH

          MOV R2,#82H

QUSHU: LCALL CUNTAI ; Restore the data stored in the ten keys 0-9

          INC R2

          INC R2

          DJNZ R0,QUSHU

   (2) Write data into 93C46

       LCALL INSB ; write enable

        MOV A,#30H

        LCALL WRI

        LCALL INSB ; write operation

        MOV A,#40H

        ORL A,#40H

        LCALL WRI ; call the erase and write instruction

        MOV A,31H

        LCALL WRI ;Write data into 31H

        MOV A,2FH

        LCALL WRI ;Write data into 2FH

        SETB P3.2

        NOP

        NOP

        CLR P3.2  

  WAIT1:JNB P2.7,WAIT1

        MOV R0,#0AH

        MOV R1,#4AH

        MOV R2,#42H

  XIERU:LCALL BAOHU ;Write the data of radio stations 0-9 into the corresponding storage units

        INC R2

        INC R2

        DJNZ R0,XIERU

        LCALL INSB

        MOV A,#00H ; write disabled

        LCALL WRI

        SETB P3.2        

4.4 Program operation monitoring part

The watchdog circuit mainly requires the MCU P3.6 to output a pulse every once in a while (less than 10 pulse intervals) to reset the counter CD4017, so that the QA terminal of CD4017 cannot become a high level, indicating that the MCU is working normally. The program is as follows:

WATCHDOG:CLR P3.6        ;复位WATCHDOG

       LCALL DELAY10 ;Call delay

       SETB P3.6 ; Allow WATCHDOG to start working

       LCALL DELAY10

       JNB P3.6, WATCHDOG ; Waiting for query

       RIGHT

Chapter 5 Test Methods and Data

5.1 Test instruments

Panasonic FM/AM V-P8177A10 signal generator HP54520A, 500M digital storage oscilloscope DF93094-Y2 digital multimeter, DF1647 signal generator.

5.2 Machine performance test

A Maximum undistorted power test, the test block diagram is shown in the figure. The output carrier frequencies of the FM signal source are 88, 96, 102, and 108MHz respectively, and the modulation frequencies are 100Hz, 1KHz, and 1.5KHz. The input level is 2mV. The FM signal is added to the BPF bandpass filter. The receiver is tuned at 88MHz, 96MHz, 102MHz, and 108MHz respectively. Change the volume potentiometer to minimize the voltage waveform distortion at both ends of the load (8 ohms). Note the voltage U0 at both ends of R2, press P=U2/R, and calculate the maximum undistorted power. The data is shown in the following table

B. Sensitivity test: The method is similar to the maximum undistorted power test. Adjust the volume potentiometer to make the receiver output power 100mW, reduce the signal source output amplitude, and make the output waveform just undistorted. At this time, the output voltage of the FM signal source is the sensitivity, and the data is shown in the table below:

C. Image rejection ratio test block diagram is shown as follows:

First measure the signal source output recording sensitivity level, the intermediate frequency output voltage when there is no modulation signal, change the frequency to the mirror frequency corresponding to each frequency point, adjust the output level of the signal generator to increase the intermediate frequency output voltage to the original standard measurement. The ratio of the two FM signal source output voltages before and after is expressed in DB, which is the image suppression ratio.

The data is shown in the following table:

5.3 Functional Testing

① It can realize full frequency range search and select stored radio stations.

②It can realize the search and selection of stored radio stations in a specific range.

③It is possible to call any stored radio station.

④With carrier display function.

Chapter 6 Circuit Fabrication

This design makes the system on three printed boards: key display board, single chip system board and radio board. Each functional board contains the components of each functional block and the corresponding auxiliary devices. The production requirements and rules are based on the following:

•   Principles of component layout on printed circuit boards
  

The quality of the layout of components on the printed circuit board directly affects the performance of the entire machine. The basic principles to consider are:

• In general, all components should be placed on the side that is basically not welded to facilitate installation, welding, debugging and maintenance.

• The components on the radio board should be arranged in circuit order as much as possible, and the circuit should be arranged compactly and densely to shorten the leads. This is especially important for high-frequency circuits.

• When arranging the spacing of components, the potential gradient between them should be considered to prevent arcing and sparking. While ensuring performance, the layout of components should be parallel or vertical to achieve neatness and beauty.

• A complete circuit should be installed on one circuit board as much as possible. If the circuit is complex or requires shielding, and needs to be divided into several printed circuit boards for installation, each complete circuit with independent functions should be placed on the same board.
  

•   Technical requirements for component installation
  

        The distribution of components on the printed board should be as uniform as possible, with consistent density. Oblique, three-dimensional cross and overlapping arrangements are not allowed. The component housing and leads should ensure a safe gap of about 1mm. There should be a reasonable gap of 0.2~0.4mm between the pin diameter of the component and the solder hole diameter of the printed circuit board, which should not be too large.

•   Principles of printed circuit board wiring
  

• The common ground wire is arranged at the edge of the printed circuit board, and an appropriate distance is left from the ground wire to the edge. Except for one side of the lead wire, the other sides are usually laid with ground wires. The power line and the corresponding filter circuit are arranged close to the ground wire, which can reduce the interference caused by the coupling of the power line and is conducive to grounding. The ground wire of each unit should generally form a loop, but have a common grounding point, so as to avoid inter-level interference caused by ground current. In addition, the ground wire is generally not made into a closed loop, so as not to form a coil that generates electromagnetic interference under the action of the magnetic field.

• The main circuits are usually arranged on the printed circuit board in units. Each functional part is as independent as possible, the leads are as short and straight as possible, and the input and output leads are separated and as far away as possible. The control lines of the microcontroller are generally arranged in parallel groups, and are as straight, neat and beautiful as possible.

• In places where frequent testing is required, some separate test points should be set up to facilitate debugging and maintenance.
  

Chapter VII Test Results Analysis and Improvement Measures

    Due to limited conditions (lack of instruments such as field strength meters), the test method we used is not very perfect, but the test results reflect the function of the FM radio we designed to a certain extent. The sensitivity of each frequency point is different. We analyzed that it may be due to the different sensitivity of the input bandpass filter to the attenuation of signals of different frequencies. The receiver has a high image suppression ratio. We believe that the bandpass filter at the input end of the antenna plays a big role.

Judging from the functions realized by the devices used in this FM radio, there are still areas that can be improved and perfected, such as the use of LCD display to provide Chinese character information, adding time display, and the use of composite keys for function keys to reduce the number of keys. From the perspective of power supply for the entire machine and ease of carrying, the entire machine should use a lower power supply.

In general, the receiving performance of this design has met the requirements, some have far exceeded the requirements of the topic, and the control function is basically complete.

                       Conclusion

Through the graduation project of this subject, I have basically mastered the working principle and application of phase-locked frequency synthesis technology, understood the working principle of radio and the measurement and debugging methods of high-frequency circuits, mastered the simple control of equipment using single-chip microcomputer system, and understood the ideas and methods of programming related single-chip microcomputer programs. Due to the time constraints and insufficient experimental conditions, this design needs to be further improved. Through this graduation project, I feel that I have exercised my abilities, learned knowledge, and benefited a lot.

Here, I would like to express my sincere gratitude to Teacher Li Jie for his careful guidance and thoughtful answers, which enabled me to successfully complete this design.